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/* SPDX-License-Identifier: GPL-2.0 */
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <dirent.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <stdlib.h>
#include <sys/select.h>
#include "gcc-compat.h"
#include "err.h"
#include "log.h"
#include "str.h"
#include "file.h"
#include "sig.h"
static int signal_pipe[2];
/*
* Initialize the signal subsystem.
*
* This function creates a pipe, the signal pipe, to deliver pending signals to
* the application (Bernstein's trick). It is called at startup, followed by
* subsequent calls to install_sighandler() for each signal that should be
* caught.
*
* signal_init() installs a generic signal handler which is used for all
* signals simultaneously. When a signal arrives, this generic signal handler
* writes the corresponding signal number to the signal pipe so that the
* application can test for pending signals by checking the signal pipe for
* reading, e.g. by using the select(2) system call.
*
* This function either succeeds or calls exit(2) to terminate the current
* process. On success, the file descriptor of the signal pipe is returned.
*/
int signal_init(void)
{
int ret;
if (pipe(signal_pipe) < 0) {
ret = -ERRNO_TO_DSS_ERROR(errno);
goto err_out;
}
ret = mark_fd_nonblocking(signal_pipe[0]);
if (ret < 0)
goto err_out;
ret = mark_fd_nonblocking(signal_pipe[1]);
if (ret < 0)
goto err_out;
return signal_pipe[0];
err_out:
DSS_EMERG_LOG("%s\n", dss_strerror(-ret));
exit(EXIT_FAILURE);
}
/* Write the signal number to the signal pipe, abort on errors. */
static void generic_signal_handler(int s)
{
/*
* Signal handlers that make system calls must save a copy of errno on
* entry to the handler and restore it on exit, to prevent the
* possibility of overwriting a errno value that had previously been
* set in the main program.
*/
int save_errno = errno;
ssize_t ret = write(signal_pipe[1], &s, sizeof(int));
if (ret == sizeof(int)) {
errno = save_errno;
return;
}
if (ret < 0)
DSS_EMERG_LOG("%s\n", strerror(errno));
else
DSS_EMERG_LOG("short write to signal pipe\n");
exit(EXIT_FAILURE);
}
/*
* If there is a child to reap, return its pid and exit status via the pointer
* arguments.
*
* Returns a negative error code on errors, zero, if there was no child to
* reap, one if a child was reaped successfully. Only if the function returns
* one, the contents of pid and status are meaningful.
*/
int reap_child(pid_t *pid, int *status)
{
*pid = waitpid(-1, status, WNOHANG);
if (!*pid)
return 0;
if (*pid < 0)
return -ERRNO_TO_DSS_ERROR(errno);
if (WIFEXITED(*status))
DSS_DEBUG_LOG("child %i exited. Exit status: %i\n", (int)*pid,
WEXITSTATUS(*status));
else if (WIFSIGNALED(*status))
DSS_DEBUG_LOG("child %i was killed by signal %i\n", (int)*pid,
WTERMSIG(*status));
else
DSS_WARNING_LOG("child %i terminated abormally\n", (int)*pid);
return 1;
}
/*
* Install the generic signal handler for the given signal, return 1 on success
* and -E_SIGNAL_SIG_ERR on errors.
*/
int install_sighandler(int sig)
{
DSS_DEBUG_LOG("catching signal %d\n", sig);
if (signal(sig, &generic_signal_handler) != SIG_ERR)
return 1;
return -E_SIGNAL_SIG_ERR;
}
/*
* This should be called if the fd for the signal pipe is ready for reading.
* It returns the number of the next pending signal. If the read was
* interrupted by another signal, the function returns 0. On errors, a negative
* error code is returned.
*/
int next_signal(void)
{
int s, err;
ssize_t r;
r = read(signal_pipe[0], &s, sizeof(s));
if (r == sizeof(s)) {
DSS_DEBUG_LOG("next signal: %d\n", s);
return s;
}
err = errno;
assert(r < 0);
if (err == EAGAIN)
return 0;
DSS_ERROR_LOG("failed to read from signal pipe\n");
return -ERRNO_TO_DSS_ERROR(err);
}
/* Close the signal pipe. */
void signal_shutdown(void)
{
close(signal_pipe[1]);
}
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